The present invention pertains to methods and apparatus for reducing or eliminating sludge bulking in waste treatment processes. In particular, the present invention is directed to methods and apparatus which encourage the selective growth of nonfilamentous organisms in aerobic waste treatment processes.
Aerobic wastewater treatment processes use an aerobic slurry of microorganisms referred to as an activated sludge to remove carbonaceous wastes by metabolic decomposition. Sludge bulking is the formation of voluminous nonsettling sludge due to excessive filamentous microorganisms. The organism frequently associated with sludge bulking is a filamentous bacteria designated type 021N (in the sense of Eikelboom, D. H., "Filamentous Organisms Observed in Activated Sludge," Water Res., G.B.N. (Volume 9, 365) (1975).
The performance of an activated sludge process is determined by two considerations. The first consideration is the oxidation and conversion of colloidal and dissolved organic matter in the suspended microbial mass. The second consideration is a physical separation of the resulting microbial mass from the liquid by settling. For many activated sludge systems, the effectiveness of the physical separation of the resulting microbial mass from the liquid by settling may be rate limiting.
The settling properties of activated sludges have been related to several different factors. One of the most important factors is the relative number of filamentous and flocculent microorganisms in the activated sludge. Excessive numbers of filamentous organisms produce low settling velocities and high compaction values. Small numbers of filamentous organisms produces large flocs with high settling velocities and low compaction values.
Although several remedies for sludge bulking have been suggested and frequently attempted, they are largely ineffective. Usually sludge bulking persists for months in aerobic waste treatment processes until largely unknown factors cause the disappearance of the filamentous organisms.